The Thermodynamics of Deer – 2.0

Cooling a deer in difficult conditions takes work. And ice.

When it comes to the thermodynamics of deer I think back to when an HVAC contractor once explained to me that air conditioning is not about adding cold air to a house, but removing the heat that is there already. That made no sense to my carpenter’s brain.

He patiently explained, “The natural state of everything is cold. We can only add or subtract heat. Air conditioning is about removing the heat added by solar gain and ambient exterior temps by utilizing some principles of physics in expanding and contracting gases to pull heat out of the air inside the house and sending it outside.” 

If you say so.

Nevertheless, I took away one very important lesson: you can only remove heat, not add cold.

This lesson comes into play for cooling a deer carcass. A deer is only warm because of metabolic processes, meaning muscle activity and digestion. As long at it eats and moves around, it’s warm. When you as the hunter put a stop to that, the deer will almost immediately start to cool down. Heat is no longer being added. The one process that will continue after death is digestion. Deer are ruminants and their stomach functions as a fermentation vat. The fermentation process doesn’t stop but just by field dressing a deer, you remove this internal heat source.

Now there is no heat being added. The deer carcass will cool down rapidly at this point, even if the air temperatures are in the 70s and 80s. The problem, however, is that the carcass cannot drop below that air temperature because of the pesky Second Law of Thermodynamics.

For decades, hunters have known that skinning the deer will help cool it down by removing the insulating pelt and exposing more tissue to evaporative cooling. This is your best bet if you are in a pack-out situation. Skin and quarter your game to reduce the relative mass-to-surface area. Hang the meat if possible to maximize the exposure to the effects of wind chill.

Game bags are invaluable for this purpose. They will protect the surface of the quarters from dirt and insects, but will wick moisture and evaporate it to provide maximum cooling from the available temperatures. If you don’t have game bags, you’re going to have to make a judgment call. You can either leave the hide on to protect the meat or you can skin and deal with surface dirt later.

This brings us back to the topic of skinning.

I do not skin my deer until I am ready to quarter and put it into coolers for transport or aging. Some people feel strongly about this. I’m not going to argue. This is how I do it and it seems to work well. The hide protects the meat from everything—heat, cold, insects, dirt—just too well for me to discard it without good reason.

One time in Wyoming, we hung some antelope in a rancher’s root cellar. The temps were running about 25 degrees at night and getting into the 60s in the afternoon, but the cellar remained in the mid-30s. Everything was great, except for one thing. Insects were active outside and could tolerate the cold for brief periods. Yellow jackets kept venturing in to eat at the exposed flesh of the flanks. But that wasn’t what bothered me. What bothered me was the appearance of the large white, rice grain-shaped objects along that same meaty fringe of the field dressing cuts. Fly larvae. Ugh! As disturbing as they were, we just cut away a generous part of the affected area and gave it no more thought. I always wonder just how bad it could have been if the whole surface of the pronghorn had been exposed!

Let’s say there are three levels of temperature and go from there.

There’s Cold Enough at less than 45 degrees.

At this temperature, you can manage cooling the carcass without using outside sources. The second is Borderline at 46 to 54 degrees and requires some cooling, though you can leave the hide on. The third would be No Way at 55 and above. At these temps, you simply cannot leave things to run their course since that would lead to putrefaction (rotting) of the meat.

If you’re working out of a vehicle with access to power or stores, ice and refrigeration are your best options.

If you’re in the Borderline zone, ice is a huge help.

When I set up a deer camp that is far from town and I know from the forecast that temps are going to be in this borderline area, I always buy 100 pounds of ice to seal in a cooler. With the deer hanging by its hind legs, you can fit 20 pounds or more of bagged ice in the body cavity. If you’re using a gambrel, it’s easy to balance a 10 pound bag on the hams to cool down all the densest parts of the deer. This will hold a deer overnight and into the next day. You get to have a good night’s sleep and work on skinning and quartering in the daylight. It might often mean you can go back out hunting that morning before returning to camp for the necessary work.

If you’re in the No Way zone, there is no waiting.

You will need to skin and quarter the deer that same day, maybe within hours. Then you can put the quarters on ice in a cooler. This should be done just like meat in a deli case. Put ice in the bottom of the cooler with an open drain plug and meat on top. Meat submerged in water isn’t a great idea usually, but there are always exceptions. More on that later.

Finally, if you have the means to do this, you can refrigerate the meat to cool it. On western hunts, I saw many a flatbed trailer that had a small generator, a chest freezer, and other gear going down the road. Hunters would use the generator to power the freezer, place quartered meat in the box, and then the well-insulated unit becomes the cooler on the way home. For those of us without all that equipment, you can usually get them at a deer processor. In my next article, I will discuss the pros and cons of using a processor to help you bring your harvest from field to table.

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Last modified: January 11, 2019

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